The etiology of health disparities involves a complex web of factors that interact to produce detrimental health outcomes for particular segments of society. In the United States, the current landscape of human immunodeficiency virus (HIV) continues to be shaped by disparities in case distribution, as African Americans (AA) account for more new HIV cases and HIV related deaths than any other racial/ethnic group. Importantly, there were more new HIV infections (52%) among young AA men who have sex with men (MSM; aged 13-29 years) than any other racial/ethnic-sexual orientation/behavior group. Recent studies have found that geographical and neighborhood environments (with environment broadly understood to encompass both physical and social attributes) are associated with sexual behavior and HIV prevalence and incidence. Although the possible role of geographic and neighborhood contexts in HIV has often been emphasized, rigorous investigations of environmental factors are rare. This is due, in part, to the sensitive nature of residential address information of HIV-infected persons and difficulties in identifying and characterizing the relevant social and physical environments. The overall aim of the Geographic and Neighborhood Study of HIV (GANSH) is to examine the associations between geospatial and neighborhood environmental characteristics and psychosocial factors and prevalent HIV/STI among AA MSM in the Jackson, MS metropolitan statistical area (Jackson MSA). The proposed study uses a cross-sectional, multi- level design to examine these associations. Non-linear (i.e., a dichotomized outcome variables) relationships between geographic and neighborhood characteristics and measures of HIV/STI status will be examined using multi-level models with a random neighborhood intercept and random covariate effects. Empirical Bayes and Geographic Information Systems (GIS) methods will be used to estimate and map the area-specific relative risk of HIV as well as the spatial distribution of the associations between behavioral and psychosocial factors and HIV/STI status. To our knowledge, this is the first study to examine the associations between geospatial and neighborhood characteristics and psychosocial factors and prevalent HIV/STI in AA MSM. The proposed research will provide answers to a wide range of questions of public health importance with direct implications for disease prevention. Moreover, results from the proposed study may change the methodological/theoretical concepts of existing HIV/STI interventions and/or prevention research. PUBLIC HEALTH RELEVANCE: HIV/STI research has traditionally focused on individual-level risk factors such as behaviors, and more recently, socio-cultural factors. The conceptual framework for the Geographic and Neighborhood Effects on HIV Study is based on the socio-ecological model, which integrates the complex interaction between individual, relationship, community, and society-level factors and allows for the consideration of factors at multiple levels in an individual's risk for experiencing or increasing HIV/STI risk. Results from this study will provide critical information in the understanding of HIV/STI risk among AA MSM and identification of high-risk areas to target for disease prevention.